In the field testing of contacts employed in such circuits as intrusion alarm circuits, a major problem arises in connection with contacts that gradually deteriorate. Resistance builds up. The contacts become loose. Either of these defects increase the incidence of false alarm. Field testing of these contacts is difficult and time consuming. Yet the value of an alarm system is a function of the maintenance that is given the alarm system. If the cost of maintenance becomes prohibitive, there is a tendency to allow the alarm system to deteriorate and thus become much less useful.
Accordingly, it is a major purpose of this invention to provide a simple and sure system of checking for defective contacts in the field particularly in equipment such as intrusion alarms.
It is a further purpose of this invention that the faulty contact detecting equipment be simple to use and easy to maintain so that it is relatively inexpensive. Furthermore, it is important that such equipment permit ready use in situations where the contact being tested is in a relatively inconvenient place. For example, the contact might be placed on a window frame that is a considerable distance from the floor and that requires a ladder for access to it. In such a case, it is important that the maintenance person be able to quickly and simply check for the defects without having to make a lot of adjustments or engage in significant calculations during the testing process. Accordingly, it is a purpose of this invention to provide a fault detector that is simple to use and provides relatively unambiguous indications of faulty conditions.
The two major ways in which a contact slowly develops faulty operation is through the buildup of resistance across the contact and through increasing susceptibility to being temporarily open when vibrated or subjected to shock. Accordingly, it is a further purpose of this invention to provide a fault detection system which will detect both of these faulty conditions.